Question 318600
You have two equations to set up : A volume equation and a concentration equation.
Let X be the amount of 10% alcohol you need.
The total volume is,
{{{6+X=6+X}}}
Not very exciting or useful with this problem.
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The concentration is
{{{60(6)+10(X)=30(6+X)}}}
{{{360+10X=180+30X}}}
{{{20X=180}}}
{{{X=9}}}
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Add 9 liters of 10% alcohol to the 6 liters of 60% to make 15 liters of 30% alcohol.